What are ectothermic animals?
Ectothermic/poikilothermic animals:
- Most invertebrates, fish, reptiles and amphibians
- Body temperature varies with the temperature of the environment
- Derive their body heat mainly from their surroundings
What are endothermic animals?
Endothermic/homeothermic animals:
- Mammals and birds
- Body temperature maintained within +/- 2˚C despite wide variation in environmental temperature
- Derive body heat mainly form metabolism
Why is maintenance of body temperature important?
- Biochemical reactions are sensitive to temperature
- Rates of enzyme reactions are dependent on temperature
- Most homeotherm enzymes have an optimum temperature close to core temperature
How is body heat gained?
Metabolic heat – from metabolism, exercise and shivering
Environmental heat – from radiation and conduction
How is body heat lost?
Radiation
Conduction
Convection
Evaporation
Distinguish shell and core temperature.
Shell temperature – temperature close to the skin, varies with temperature of environment.
Core temperature – brain and internal organs, less variation in temperature.
How does the cardiovascular system control shell and core temperatures?
CVS system controls this, the blood flow determining where blood is, shunted in the core to conserve temperature or in the periphery to give off heat.
What is thermoneutral zone?
Thermoneutral zone is where ambient temperature is influencing skin temperature only to the degree of moving blood in the body, no mechanisms for cooling or metabolism, shunting blood around alone is enough to maintain body temperature. So animals kept here so energy is not wasted and energy is all used for growing meat, producing milk or eggs.
Describe the negative feedback control system of temperature.
Thermosensors measure temperature in the skin and core. They feed information in into a controller, the hypothalamus. There are 2 distinct areas in the hypothalamus that control temperature. Hypothalamus will send out demands when it is comparing the inputs to a fixed set point. Any deviations from the set point will cause effector mechanisms to initiate mechanisms of heat loss or gain.
What are cutaneous thermoreceptors?
Cold and warm receptors. Free nerve endings that are temperature sensitive.
What are core thermosensors?
Central blood vessels (great veins) and abdominal viscera. These multiple thermosensors may permit finer control of core temperature.
What is the other form of thermosensor?
CNS thermosensors
Describe the role of the carotid rete in brain cooling.
- When information comes into the hypothalamus, it is able to regulate any changes that must occur for constant core temperature.
- Brain must maintain a constant temperature itself as neurones are very sensitive to temperature.
- Animals, not so much in primates, have a carotid rete, a counter current exchange system by which the brain maintains a constant temperature despite fluctuations in the body temperature.
- Cold air inhaled cools surrounding blood in the nasal cavities.
- This cools warm blood from the core through the arterial system, in opposite direction to arterial blood.
- So when blood leaves the rete mirabile, means the blood exiting the brain is cooler.
What are the hypothalamic roles of the preoptic area in temperature?
Heat-losing centre:
- Vasodilation to increase blood flow to skin
- Sweating
- Increased respiration through the mouth
- Inhibits heat promoting centre
What are the hypothalamic roles of the posterior nucleus in temperature?
Heat-promoting centre:
- Vasoconstriction
- Shivering thermogenesis
- Non-shivering thermogenesis
- Inhibits heat-losing centre
How is body temperature maintained?
Metabolic responses – below thermoneutral zone
Vasomotor responses – within thermoneutral zone
Evaporative responses – above thermoneutral zone
Describe the role of counter current heat exchange in regulating temperature.
Warm blood from the core, oxygenated through arteries and out of the periphery. If there is a large temperature differences, the counter current flow will lose heat via conduction, convection and radiation. Because the artery and vein are in close proximity, there is direct heat exchange between them and less heat is lost as the warmer artery leaves the core. This is important in all animals but especially for penguins, who have very adapted counter current flow systems in their feet s they do not freeze.
What are the mechanisms for preventing heat loss?
Insulation
Piloerection
Voluntary movements and behavioural responses:
- Postural changes that reduce surface area
- Movement into a warmer environment
- Increasing muscle activity
- Long term behaviours
What are the mechanisms for heat production?
Metabolism – most of the chemical energy is lost as heat
Shivering thermogenesis – rapid involuntary cycle of contraction and relaxation of muscles
Non-shivering thermogenesis – stimulation of metabolism in brown adipose tissue
How does sweating regulate body temperature? How does sweating affect other homeostatic measures?
- Evaporative processes for cooling
- Innervation by the sympathetic nervous system to sweat glands in the dermis
- Sweat glands produce a primary secretion that is isotonic to plasma so it has the same composition in terms of salt and water as blood.
- As this isotonic secretion comes up through the sweat duct, sodium and chloride is reabsorbed
- This is to conserve salts and water in the body as we do not want to lose these, only the heat.
How does panting regulate body temperature?
Only utilised in thin coated animals or animals that do not have sweat glands.
- Takes in cooler dry air through the nose, passing over the turbinate bones and hard palate, where it picks up heat from the blood. Also passes along humid tongue, which is also hot.
- Excess water vapour is saturated with heat and so heat is lost through evaporation.
- Occurs in shallow rapid ways
- Uses rapid natural oscillation of respiratory muscles to saturate air with water vapour.
- Does not increase ventilation rate as air is not being blown down into the lungs.
How does peripheral vasodilation regulate body temperature?
Reduced sympathetic stimulation causes blood vessels in the periphery to open up so more blood shunts to the surface and heat can be dissipated by direct transfer, convection and radiation.
What is the role of arteriovenous anastomosis in regulating body temperature?
Arteriovenous anastomosis can open up in higher temperatures, while blood can go to the dermis to dissipate heat through the skin. In low ambient temperature, hairs are raised to trap a thin layer of air for insulation and reduce blood flow to the dermis and the heat loss.
How can insulation be used to keep an animal cool?
Insulation, like fur, feathers and wool, can keep animals cool in hot environments as it can be a barrier between heat being trapped by the body.
